1. Field of the Invention
The present invention relates to optical cross-connects, and particularly to scalable and mass-manufacturable OXC systems and components using liquid crystal.
2. Description of the Prior Art
In optical networks, optical fibers are interconnecting a variety of optical network elements (ONE) using a wide range of network configurations. Some of basic ONE include optical cross-connect (OXC), optical add/drop multiplexer (OADM), and optical terminal multiplexer (OTM).
The OXC is an essential ONE to construct general mesh or ring networks, while the OADM and OTM are useful for ring and linear networks. OXC can be classified as fiber cross-connect (FXC), wavelength selective cross-connect (WSXC), wavelength interchange cross-connect (WIXC), and hybrid OXC. This classification is based on the ability/inability to cross-connect on a per wavelength basis and the level of wavelength conversion provided. FXC is a simplest form of OXC, while WSXC and WIXC are becoming increasingly complex by delivering additional functionality.
FXC delivers a multiport fiber switching to enable cross-connection of multiwavelength optical signals as a group without demultiplexing individual signals. For FXC, there is no requirement for single channel add/drop, regeneration, optical amplification, performance monitoring, protection switching, DWDM signal grooming, and communication protocol support & routing, while WSXC and WIXC requires all of these functions. Additionally, WIXC requires a wavelength interchange function.
Hybrid OXC is based on combining any of FXC, WSXC, or WIXC functionalities. All of these OXCs desirably should support configuration management, fault management, and security management functions. Essential criteria on evaluating OXC are: (1) port counts, (2) device scalability, (3) blocking characteristics, (4) cost, (5) footprint size, (6) power consumption, (7) insertion loss, (8) uniformity, and (9) other optical performance parameters.
While OXC is an integral optical network element (ONE) for reconfigurable optical networks, the building blocks for known OXC include numerous photonic & electronic components such as single-mode fiber optic switch, DWDM mux/demux filter, wavelength converters, optical amplifiers, optical performance monitors, optical transponders, and OXC controllers. Optical performance parameters for reliable and compatible operation of single-mode fiber optic switches include optical passband, insertion loss, uniformity, wavelength flatness, control stability, repeatability, polarization dependent loss, crosstalk, directivity, return loss, differential group delay, maximum allowable optical power, and switching time. The optical passband parameter classifies the fiber optic switches into single band (covering either 1260 nm to 1360 nm OR 1480 nm to 1580 nm), dual band (covering both bands), or wideband (covering 1260 nm to 1580 nm).
Reliability is also a primary concern, including mechanical integrity, endurance, and special test procedures. Mechanical integrity requirements may include ability to withstand mechanical shock, vibration, thermal shock, solderability, and fiber integrity. The endurance requirements are for dry high-temperature storage, damp high-temperature storage or damp heat (hermetic), damp high-temperature storage or damp heat (non-hermetic), low-temperature storage, temperature cycling, and cyclic moisture resistance. Special tests may include inter moisture and electrostatic discharge (ESD) tests.
The OXC can reconfigure the optical network dynamically by interconnecting arbitrary input ports to any designated output ports. There exist a variety of non-blocking cross-connect network architectures, such as cross-bar network, Spanke network, Clos network, and Benes network. The cross-bar, Spanake, and Clos networks can be classified as fully non-blocking networks, while the Benes network is a rearrangeably non-blocking network. The fully non-blocking cross-connect architecture represents a network, where any unused input port can be connected to any unused output port without disrupting the existing interconnects within the network. In contrast, the rearrangeably non-blocking network may require the existing interconnects to be broken down and rearranged in order to accommodate new interconnects among unused input and output ports.
The Spanke network provides the desirable fully non-blocking characteristics and it is composed of three distinctive stages: 1) N arrays of 1×N switches, 2) N2 cross-connect network, and 3) N arrays of N×1 switches. The N2 cross-connect network staged at the middle is passive but massively parallel cross-point interconnects, wherein the N2 output ports from N arrays of 1×N switches interface the N2 input ports for N arrays of N×1 switches. The Spanke network is known to be capable of furnishing small signal crosstalks and simple control algorithms to the OXC. However, the known drawback of this architecture is an excessively large N2 cross-connect network at the middle stage, especially when the port-count N becomes very large. Nevertheless, FIG. 1 shows that any input port can be routed to any output port in a fully non-blocking manner in a Spanke network.